Recently, one of the main research areas in the field of tyres concerns a possible substitution of zinc oxide (ZnO) as the vulcanization activator.
Due to its possible environmental implications, there is a requirement for the use of ZnO to be limited. Obviously, an excessive limitation of the ZnO, although on the one hand it would meet the environmental requirements, on the other may compromise the vulcanization of the compound with negative consequences in terms of physical and/or dynamic characteristics of the resulting compounds.
The need was therefore felt for an alternative to the use of ZnO in rubber compounds, which meets the environmental requirements without altering the vulcanization of the resulting compound and, consequently, compromising its physical and/or dynamic characteristics.
The Applicant has unexpectedly found that a particular class of zinc salts is able to fully substitute the presence in the compound of the ZnO as the vulcanization activator and, at the same time, maintain unchanged the rheometric and mechanical characteristics of the resulting compound and significantly reduce the overall quantity of zinc in the compound.
In particular, the Applicant has surprisingly found that a class of Zn salts, originally tested as processability adjuvants, have unexpected properties as vulcanization activators. It has been ascertained that the activity of these Zn salts as vulcanization activators is such as to permit complete substitution of the ZnO.